The brilliant detective has gathered all the suspects in the drawing room for the grand reveal. Select ALL the grammatically correct ways she can structure her dramatic accusation.
The correct answers are What the butler hid in the grandfather clock was the diamond. and The diamond is what the butler hid in the grandfather clock.
Wh-cleft sentences can be constructed in the standard order (What-clause + be + focused element) or reversed (Focused element + be + what-clause). Both options correctly isolate "the diamond" for dramatic emphasis.
The incorrect options contain structural errors: "What did the butler hide" incorrectly uses question word order inside a noun clause; "the thing what" is non-standard (it should be "the thing that"); and "were" is incorrect because the focused element "the diamond" is singular.